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2016
Development of an energy-harvesting magnetorheological fluid damper
Yun Lu University of Wollongong
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Recommended Citation Lu, Yun, Development of an energy-harvesting magnetorheological fluid damper, Master of Philosophy thesis, School of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, 2016. https://ro.uow.edu.au/theses/4738
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Development of an Energy-Harvesting Magnetorheological Fluid Damper
A thesis submitted in fulfillment of requirements
for the award of degree of
Master of Philosophy
Yun LU
Faculty of Engineering and Information Science, University of Wollongong
August 2016
Wollongong, New South Wales, Australia
CERTIFICATION
I, Yun Lu, declare that this thesis, submitted in partial fulfilment of the requirements for the award of Master of Philosophy, in the School of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, is wholly my own work unless otherwise referenced or acknowledged. The document has not been submitted for qualifications at any other academic institution.
Yun Lu
22th July 2016
ACKNOWLEGEMENTS
ACKNOWLEGEMENT
I wish to thank my supervisors, Prof. Weihua Li and Prof. Guoliang Hu, for their enthusiastic support, professional direction and constant encouragement that inspired me to overcome the challenges on my road of study.
Particular thanks are extended to Shuaishuai Sun and Xin Tang for their help on operating of laboratory facilities and Labview programing. Without their assistance of my lab mates, I could have a lot of problems to complete this dissertation. I thank all who helped me during my studies.
Finally, I especially would like to thank my parents for their understanding, patience and unwavering support of my studies.
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TABLE OF CONTENTS
TABLE OF CONTENTS ACKNOWLEGEMENT i TABLE OF CONTENTS ii LIST OF FIGURE iv LIST OF TABLE vi Abstract 1 CHAPTER 1 INTRODUCTION 2 1.1 BACKGROUND AND MOTIVATION 2 1.2 OBJECTIVES AND SCOPES 3 1.3 THESIS OUTLINE 4 CHAPTER 2 LITERATURE REVIEW 5 2.1 INTRODUCTION 5 2.2 MR TECHNOLOGY 6 2.2.1 MR Fluid and MR Effect 6 2.2.2 The Working Modes of MR Damper 7 2.2.3 Damping Force Model for MR Damper 8 2.3 ENERGY HARVESTING THECHONOLOGY 17 2.4 SELF-SENSING THECHNOLOGY 19 2.5 CHAPTER SUMMARY 22 CHAPTER 3 DESIGN OF EHMR DAMPER 23 3.1 KEY CONSEPTION AND WORKING PRINCIPLE 23 3.1.1 The Operation Principle of the Prototype 23 3.1.2 Consideration in Structure Design 24 3.2 MATERIALS USED IN DESIGN 27 3.3 CONFIGURATION OF THE EHMR DAMPER 31 3.3.1 Modelling of the MR Damper 31 3.3.2 The Simulation Based on Finite Element Method 36
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LIST OF FIGURES
3.4 CONFIGURATION OF LINEAR POWER GENERATOR 38 3.5 DEVELOPMENT OF A SELF-SENSING ALGORITHM 43 3.6 CHAPTER SUMMARY 47 CHAPTER 4 PROTOTYPING AND TESTING OF EHMR DAMPER 48 4.1 FABRICATION AND ASSEMBLING OF PROTOTYPE 48 4.2 TESTING PROCESS 51 4.3 THE PERFORMANCE OF EHMR DAMPER 52 4.3.1 Testing of the Damping Property 52 4.3.2 Modeling of Damping Force 56 4.3.3 Identification of Damping Force Modeling 61 4.4 THE PERFORMANCE OF THE ENERGY HARVEST CAPABILITY 64 4.4.1 Performance of the Linear Generator 69 4.4.2 Frequency Multiplication Effect 71 4.4.3 Performance of Energy Harvest Effect via Rectification 71 4.5 THE PERFORMANCE OF SENSING CAPABILITY 74 4.5.1 Comparison Between Guessed Voltage and Initial Measurement 74 4.5.2 Sensing of Velocity and Displacement 74 4.5.3 Discussion of Self-sensing Result 78 4.6 CHAPTER SUMMARY 78 CHAPTER 5 CONCLUSION AND FUTURE WORK 80 5.1 CONSLUSION 80 5.2 FUTURE WORKS 81 REFERENCE 82 APPENDIX A: DETAILS AND CONSIDERATIONS OF UESING MTS 91
iii
LIST OF FIGURES
LIST OF FIGURES Figure 2.1 MR Effect in MR Base Materials Figure 2.2 Basic Operating Mode of MR Fluid Figure 2.3 A Coulomb Friction Element in Parallel with a Viscous Dashpot Figure 2.4 Gamota and Filisko’s modified Bingham model Figure 2.5 Schematic of simple Bouc-wen model Figure 2.6 Schematic of modified Bouc-wen model Figure 2.7 A typical shock absorber with mechanical energy harvesting system Figure 2.8 A Typical EHMR damper based on EMI technology Figure 2.9 Self-sensing technology for MR damper Figure 3.1 The schematic of EHMR damper Figure 3.2 The different between single-ended and double-ended structure Figure 3.3 The simulation of linear generator from Chen Figure 3.4 The simulation of isolation of magnetic interference Figure 3.5 Shear stress vs. shear rate under no magnetic field applied Figure 3.6 Yield stress vs. magnetic field strength Figure 3.7 Typical magnetic properties Figure 3.8 Magnetic properties of steel 1020 Figure 3.9 Magnetic properties of NdFeB permanent magnet (N52) Figure 3.10 Principle of operation of MR damper Figure 3.11 Key diagram of the basic magnetic circuit of MR damper Figure 3.12 Structure of piston head Figure 3.13 Finite element analysis of MR damper part Figure 3.14 Magnetic flux density under different applied current Figure 3.15 Magnetic flux density in the annular gap under different currents Figure 3.16 Schematic of linear power generator Figure 3.17 Equivalent magnetic circuit for the proposed power generator Figure 3.18 Distribution of magnetic density distribution Figure 3.19 Distribution of Cogging Force Figure 3.20 The principle of velocity-sensing algorithm Figure 4.1 Main components of the proposed EHMR damper
iv
LIST OF FIGURES
Figure 4.2 Main components arrangement for the prototype testing Figure 4.3 The proposed MR damper Figure 4.4 Damping force vs. amplitude under 1Hz frequency Figure 4.5 Damping force vs. excitation frequency under 5mm amplitude Figure 4.6 Damping force vs. excitation current under 5mm amplitude Figure 4.7 Force-displacement relation of the MR damper test with different current under 1 Hz, 5mm amplitude Figure 4.8 Mathematical model of MR damper based on Bouc-wen mode Figure 4.9 Matlab program for the proposed mathematic model Figure 4.10 Comparison of mathematic model and experimental data base on time-force relation Figure 4.11 Comparison of damping force based on Bouc-wen model and measurement Figure 4.12 Desired damping force from mathematical model vs. initial measured data Figure 4.13 The desired damping force when piston operates under different excitation Figure 4.14 The desired damping force from mathematic model vs. the measured data Figure 4.15 Comparison between experiment and calculation result: coils 1 Figure 4.16 Comparison between experiment and calculation result: coils 2 Figure 4.17 Generate voltage under open loop: 5mm 2Hz Figure 4.18 Generate voltage under open loop: 5mm 3Hz Figure 4.19 Generate voltage under open loop: 5mm 4Hz Figure 4.20 Comparison of generative voltage under different amplitude and frequency Figure 4.21 Frequency multiplication effect under frequency of 4 Hz and amplitude of 10mm Figure 4.22 Frequency multiplication effect under frequency of 4 Hz and amplitude of 15mm Figure 4.23 Schematic of the AC-DC rectifier Figure 4.24 Assembled EHMR damper with AC-DC rectifier Figure 4.25 The experiment result of performance of generator with AC-DC rectifier Figure 4.26 Comparison between experiment and calculation result: coils 1 Figure 4.27 Experimental result of sensing velocity under excitation of 3Hz 5mm Figure 4.28 Experimental Result of Sensing Velocity Under Excitation of 5Hz 15mm Figure 4.29 Experimental result of sensing displacement under excitation of 3Hz 5mm Figure 4.30 Experimental result of sensing displacement under excitation of 4Hz 15mm
v
LIST OF TABLES
LIST OF TABLES Table 3.1 Key parameter of the cylinder
Table 3.2 Key Parameter of the Piston
Table 3.3 Magnetic flux in each region of the piston
Table 3.4 Magnetic induction intensity of each region
Table 3.5 The magnetic field strength of each region
Table 3.6 material used in main component
Table 3.7 parameter for main structure
Table 4.1 Parameter of the fabricated MR damper part
Table 4.2 Parameter of the damping force model
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ABSTRACT
Abstract
Due to the unique property of magnetorheological (MR) effect, the MR-base device takes the advantage in rapid response, large dynamic range in strength and low energy consumption. In the last several decades, MR damper is becoming one kind of very promising smart device in the dynamic vibration control systems. It is noted in many current research that the MR damper can be integrated with the energy harvest system into one device. The energy-harvesting magnetorheological (EHMR) damper saw the possibility to produce a certain amount of energy from mechanical vibration. In some research, the recovery energy can be invoked as the dynamic signals to determine the velocity and displacement of the MR damper. As the result, the new EHMR damper saw the possibility to reduce the power consuming. This multi-function MR damper is considered to be one of the most ideal solution to improve the application of the MR- base device in lower energy requirement, better reliability and more flexible arrangement.
In this thesis, the full study is dedicated to investigate and design an EHMR damper. Conceptions, operating principle and mathematical methods in design of EHMR damper are studied. The process of design, material selecting and evaluation, numerical design methods is discussed. Finite-element analysis is investigated to evaluate the distribution of magnetic field and isolation of magnetic interference. Mathematical model is investigated and optimized to study the nonlinear mechanical property of MR fluid.
The prototype of the EHMR damper is designed, fabricated and tested. Evaluation of energy generation efficiency and self-sensing algorithm is varied out. The damping property of the EHMR damper and each individual function, including energy recovery property and self-sensing capability are experimentally validated including the dynamic working range. The power generated criterion, sensing property and sensing reliability.
The test result illustrates that the proposed EHMR damper, can provide around 350% dynamic damping range under 0.6A driving current. While the proposed energy harvest system can provide a minimized cogging force, and recover a certain amount of power, when working with the MR damper. In addition, the generated power can accurately determine the relative velocity and displacement of the damping system.
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INTRODUCTION
CHAPTER 1 INTRODUCTION
1.1 BACKGROUND AND MOTIVATION
The suspension system, as an important component in the vehicle, directly relate to the stability, safety and comfortable capability [1]. Three types of suspension systems had been widely used in unwanted vibration reducing area, which is well known as passive, active, and semi-active suspension.
From many previous applications of the suspension system, some drawback limited their application. The passive suspension with fixed spring and shock absorber, provides the simplest structure and relatively low cost, but the stiffness, inherent frequency and damping coefficient had been constant, when the particular suspension is designed. As the result, the passive suspension can work properly in a relative limited working range, but the system cannot provide optimal vibration attenuation for various conditions [2]. Thus, in order to counteract the limitation of the passive system, the active suspension was developed. In the active suspension, an additional active force such as the hydraulic system was introduced as part of the suspension to make the whole system much more responsive to disturbance. Even though, the active system provides adaptability to a large range of excitation, the complex feedback control loop could lead to a low reliability. Moreover, the complex structure, relatively high cost had limited its application in many commercial vehicles [3]. In the last several decades, due to the advance in a relatively simple structure, lower energy consumption, lower cost and better reliability, the semi-active system was found an increasingly popular in many research. Benefited the developing of smart materials, in many latest research, the MR material, especially MR fluid had been widely employed. MR fluid provides the novel MR characteristic of reversibly changing from a liquid status to a semi-solid state in million-seconds and very low control energy consuming is believed to be one of the most ideal materials. [4, 5]
Even the semi-active suspension with MR based device saw an advantage in low energy consumption and large range adaptability, many current studies shown that, the dynamic sensors, such as laser vibrameter and velocity sensor, which used in the feedback control loop, could increase the power consuming [6]. Also the kinetic energy had been wasted in vibration resistance [7]. Thus, in the latest decade, the energy harvest technology was widely proposed as the energy - 2 -
INTRODUCTION
recovery device, aiming to recover kinetic energy from dynamic movement. Furthermore, some very latest studies discussed the possibility to employ the energy recovery device as velocity or displacement sensing device, installed or utilized sensor to provide the dynamic movement of the damper, this technology is well known as self-sensing capability. As the result, the application of the semi-active system can be improved.
1.2 OBJECTIVES AND SCOPE
In previous research on EHMR damper, the electromagnetic induction (EMI) technology was widely employed. The MR damper works as the vibration reducer and the EMI device can recover the vibration energy. Manufacture and test the prototype of the EHMR damper. Moreover, alternating voltage generated by EMI device can be utilized to describe the relative velocity and displacement. However, most previous literatures only discuss the possibility of achieving self- sensing, by discussing the relation between the excitation frequency (displacement) and generated voltage, rather than directly provide the sensing result. Moreover, in some research the isolative structure that used to minimize magnetic interference from the separated magnetic field that generated by MR damper and permanent magnet array, which increase the complexity of the structure.
In this study, we proposed to design an EHMR damper with a new structure, which integrated the energy harvest capability and self-sensing capability. And the new structure can efficient deal with the problem of magnetic field interference between the MR damper and linear generator without magnetic field isolating parts, so the size of device can be reduced. The project was divided into three parts in terms of design verification and experimental testing stages. In order to test property of the design under, the frequency range choose from 1 Hz to 4 Hz, and the amplitude choose from 1 mm to 7.5 mm. Specific objectives are given as the following:
1) Design an MR damper, and its components to achieve high efficiency in energy usage. 2) Develop and optimize the mathematical model for the proposed EHMR damper. 3) Develop the self-sensing algorithms to convert the voltage signal into velocity and displacement information.
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INTRODUCTION
Scope of the Study
The scope of this study encompasses the following:
1) Study the working principle of the EMI technology and the EHMR dampers. 2) Study the mathematical modelling and its optimization. 3) Manufacture and test the prototype of the EHMR damper.
1.3 THESIS OUTLINE
This thesis begins with background, motivation and research scope in Chapter 1. Then, followed the literature review of MR technology and energy harvest technology and self-sensing technology with their applications in Chapter 2. In Chapter 3, the design of EHMR damper was presented. Then, the minimization of magnetic field interference was first briefed. Followed, the basic conception of multi-function integration and the key issue in multi-functions integrating design, including materials, structural design, and operating principle were discussed. In the simulation part, the finite element modeling for the proposed linear generator and MR damper part was investigated. Electromagnetic analysis based on Maxwell method was to be used to evaluate the magnetic field distribution and cogging force for the proposed EHMR damper. Then the Bouc- wen model and self-sensing algorithms for the proposed EHMR damper were discussed. In chapter 4, the fabrication of the proposed EHMR damper was briefed. Then, the experimental process and actuation in experiments were introduced. In the experimental and analytical part, damping property of the EHMR damper was investigated. The damping force model based on Bouc-wen model was optimized and performance of the optimized model was presented and discussed. Followed, operating property of the linear generator under different amplitude and frequency was presented. The characteristic of power generating with the AC-DC rectified was investigated. Then the sensing method was evaluated and tested under different frequency and displacement. The theoretical analysis and comparison were performed to the proposed method. The experimental results presented the feasibility and accuracy of the measurement of velocity and displacement. Finally, conclusion was summarized in Chapter 5.
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LITERATURE REVIEW
CHAPTER 2 LITERATURE REVIEW
2.1 INTRODUCTION This study aims to develop a multi-function integrated EHMR damper. In this section, some key conception should be reviewed including the MR fluid and MR effect, the mathematical model of damping force for MR damper, energy harvesting technology and self-sensing technology, At last followed by the application of the EHMR damper.
The MR damper has undergone significant development due to its unique rheological properties under exerted magnetic fields [8]. These features have led to the development of many MR-based devices such as the MR damper, MR valve, MR brake, MR clutch, and so on. Among of them, the most popular MR-based devices are MR dampers due to their long range controllable damping force, fast adjustable response, and low energy consumption. In order to improve the application of MR damper, and decrease the energy consumption in the semi-active control process. [10] EHMR dampers have received a great deal of attention due to their capability to recover the kinetic energy normally dissipated by traditional MR dampers.
In this section, a review of the literature relevant to current knowledge in the above areas is carried out. The principles and foundation of the MR systems were presented. Then some basic knowledge of mathematical method used in analysis of performance of the MR damper was presented and discussed. Followed, some latest research in MR damper with energy harvesting system was reviewed. At the last, the review of self-sensing technology was presented.
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LITERATURE REVIEW
2.2 MR TECHNOLOGY
2.2.1 MR Fluid and MR Effect MR fluid is a kind of classical smart material that consists of stable suspensions of micro-sized magnetically polarizing particles, carrier fluid, and stabilizing additives. The rheological properties of MR fluid are reversible and can be changed by applying an external magnetic field to the fluid domain [11]. While a magnetic field is absent, MR fluid remains as a free flowing liquid with a consistency similar to motor oil, and behaves like a Newtonian fluid as the particles are randomly dispersed [11]. Ideal MR fluid is proposed to possess the following features: non-corrosive, stable against settling, high magnetic saturation, and large field induced yield stress but small apparent viscosity in the absence of an applied field [13].
A simplified explanation for the development of an apparent yield stress in MR fluid is shown in Figure 2.1.When an external magnetic field is applied, MR fluids undergo a considerable increase in their apparent yield stress. Without a magnetic field, the particles are randomly dispersed in suspension and the fluid behaves as a Newton fluid (Figure 2.1.a). When an external magnetic field is applied originally magnetic particles are magnetized and become almost a single domain and behave like tiny magnets. Magnetic interaction can be minimized if the magnetic particles line up along the direction of the magnetic field (Figure 2.1.b). Although a shear stress or pressure difference is needed to disrupt this structure formed in energized MR fluids [14]. The strength of the fluid, i.e. the value of the apparent yield stress, increases as the applied magnetic field increases. The yield stress developed in MR fluids can occur in a few milli-seconds. Besides, removing the applied field makes the fluid return to its initial liquid state.
(a) No magnetic field is applied; (b) Magnetic field is applied. Figure 2.1 MR effects in MR base materials [http://www.transtutors.com/]
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LITERATURE REVIEW
Typically, this change is manifested by the development of a yield stress that monotonically increases with an applied field. Interest in MR fluids derives from their ability to provide simple, quiet and rapid response interfaces between electronic controls and mechanical systems. That MR fluid has the potential to radically change the way electro-mechanical devices are designed and operated has long been recognized [14]. The initial discovery and development of MR fluid and devices can be credited to Jacob Rabinow at the US National Bureau of Standards in the 1940s [16-18]. The physical properties of MR fluid has a huge potential for MR applications [15, 19].
2.2.2 The Working Modes of MR Damper The MR damper is a type of semi-active control device that provides controllable damping force by MR fluid. The damping force delivered from the MR damper depended on the size, the property of MR fluid and the flow pattern that applied on the MR damper. The basic MR damper’s operation pattern could be classified in: (a) valve mod (flow mode), (b) direct shear mode (clutch mode), (c) squeeze mode (compression mode), and combination of these modes [20]. For the expected damping force and displacement of MR damper are rather large, MR dampers primarily operate under valve mode. As shown in Figure 2.2 (a), MR dampers operate under valve mode when the flow of MR fluid impeded from one reservoir to another.
(a) Valve Mode (b) Direct Shear Mode (c) Squeeze Mode
Figure 2.2 Basic Operation Modes for MR Fluid [20]
Base on the principle of driving the viscosity of MR fluid, the controllable damping force is derived external magnetic field and driving current, thus the energy consuming of the damper could be relatively low, depend on the material of coils and size of the device. Therefore, by benefiting from flexible control, fast response and low power requirement, the MR damper had been draw attention on various vibration controls especially in naval gun controlling [21], field of landing
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LITERATURE REVIEW
gear [22], prosthetic knees [23], washing machines [24], high speed train suspension [35, 36], seismic vibration control of different civil structures [27, 28].
Over the last decade, research show that the mechanical energy within the kinetic vibration was wasted in heating and overcoming vibration, also those sensors that used in the dynamic responses system in suspension increase the power consuming. Moreover, increasing number of research show that, the energy within kinetic vibration could be used to support the suspension. The simulation illustrate that the dissipated energy of a passenger vehicle going through a poor roadway in 13.4m/s reach approximately 200W [29]. Researchers believe that it is a penitential energy resource to support the dynamic system and damper control.
2.2.3 Damping Force Model for MR Damper The MR fluid model and governing equation of the MR device working different modes can give a precise prediction in the design process, while in semi-active control, strategies where the hysteretic behavior must be considered, models for the MR damper based on experimental test data must be derived. Up to now, various kinds of parametric and non-parametric models, according to the properties that the developed models represent, have been developed to model the characteristics of MR dampers’ hysteretic damping force. In the following paragraphs the parametric models are reviewed.
(1) The parametric MR damper model To start with, any variation in the damping force depends not only on the applied current, but also on the excitation, including the stroke and frequency of the vibration. So the hysteretic characteristics of an MR damper may be expressed by function in current, displacement, velocity, and acceleration as follows:
퐹(푡) = 푓(퐼, 푥, 푥̇, 푥̈) (2.1) where 퐹(푡) is the damping force, I is the applied current, x is the piston displacement, 푥̇ and 푥̈ are first and second derivatives with respect to time, respectively. According to the methods used to model hysteresis, the parametric models for MR dampers can be categorized as the Bingham
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LITERATURE REVIEW
based dynamic models, the Bi-viscous models, the Viscoelastic-Plastic models, the Stiffness- Viscosity-Elasto-Slide models [30], the Bouc-wen hysteresis operator based dynamic models, the dahl hysteresis operator based models [31], the LuGre hysteresis operator based models [32-34], the hyperbolic tangent function based models [35], the Sigmoid Function Based models [36,37], the Equivalent models [38] and the Phase Transition models [39]. In the paragraphs that follow, the most applied MR damper models of the Bingham Model, the Bi-viscous Model, the Visco- elastic-plastic Model and the Bouc-wen Model are reviewed.
Bingham Model
In order to characterize the electro-rheological damping mechanism, Stanway et al [40] develop a Bingham plastic model to summarize the damping hysteresis phenomenon. In this model, it combines a coulomb friction element in parallel with a viscous dashpot, as showed in Figure 2.3, according to which the governing equation is generated as given:
푓(푡) = 푐0푥̇ + 푓푐sgn(푥̇) + 푓0 (2.2) where 푥̇ represents the velocity of external excitation, c0 is the damping coefficient of the dashpot,
fc gives frictional force component related to the field dependent yield stress and f0 is the offset due to the presence of an accumulator [41].
Combined with the Bingham plastic MR fluid model, the Bingham behaviour of MR damper can also be derived through the study of an axi-symetric model of MR fluid flow [42].
Figure 2.3 A coulomb friction element in parallel with a viscous dashpot
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LITERATURE REVIEW
The piecewise Bingham model developed by Wereley [43] is given. The equations describing the damper model are [44, 45]:
퐶푝표푠푡푥̇ + 퐹푦 푥̇ > 0
퐹(푡) = {−퐹푦 < 퐹(푡) < 퐹푦 푥̇ = 0 (2.3) 퐶푝표푠푡푥̇ − 퐹푦 푥̇ < 0
Observing Equation 2.3, if 퐶푝표푠푡 = 푐0 and 푓푦 = 푓푐, the equation will reduce to same form as show in Equation 2.2.
In the piecewise Bingham model, it is assumed that the material is rigid and doesn’t flow which means |퐹(푦)| < 퐹푦, when the shaft velocity is zero. When the force applied to the damper is larger than the yield force, the fluid starts flowing and the material is essentially a Newtonian fluid with a certain amount of yield stress.
The limitation of the Bingham model is that it assumes that the fluid remains rigid in the pre-yield region, so it cannot describe the fluid elastic properties at small deformations and low shear rates [46].
Given that either the Bingham or piecewise Bingham models could accurately describe the hysteretic loop of MR dampers, researchers have given more attention to modify the Bingham model.
One of the modified Bingham models proposed by Gamota and Filisko et al [47] focus on predicting the behavior of ER fluid, and was used to model MR damper dynamics by Spencer [41]. The governing equation is given by:
F(t ) k 1()() x 2 x 1 c 1 x 2 x 1 f 0
c0 x 1 fc sgn( x 1 ) f 0 ||Ff()tc (2.4a)
k2() x x 2 f 0
Fk(t )1211 xxc 20() xf ||Ff()tc (2.4b) kxxf220() where c0 is the damping coefficient associated with the Bingham model, and k1 , k2 and c1 are associated with linear solid material.
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LITERATURE REVIEW
This model can portray force displacement and force velocity relationships very well however the governing equations are extremely stiff, making it difficult to deal with numerically. A numerical integration of Equation 2.10a and 2.10b for the parameters given requires a time step on order of 10e-6.
Figure 2.4 Gamota and Filisko’s modified Bingham model
Bi-viscous Models
The nonlinear bi-viscous model was proposed by Wereley et al [43] by utilising a set of piecewise linear functions to construct the hysteresis loop on the basis of two different damping coefficients present the pre-and post- yield condition of MR fluid 0. The hysteresis loop defined by this bi- viscous model is given in Figure 2.6, while the governing function is presented in Equation 2.11.
퐶 푥̇ − 푓 푥̇ ≤ −푥̇ 푥̈ > 0 푝표 푦 1 퐶푝푟(푥̇ − 푉ℎ) − 푥̇1 ≤ 푥̇ ≤ 푥̇2 푥̈ > 0
퐶푝표푥̇ + 푓푦 푥̇2 ≤ 푥̇ 푥̈ > 0 푓ℎ = (2.5) 퐶푝표푥̇ + 푓푦 푥̇1 ≤ 푥̇ 푥̈ < 0 퐶푝푟(푥̇ + 푉ℎ) − 푥̇2 ≤ 푥̇ ≤ 푥̇1 푥̈ < 0 {퐶푝표푥̇ − 푓푦 푥̇ ≤ −푥̇2 푥̈ < 0 where fy is a constant derived from a projection of the post-yield branch when 푥̇ = 0, and vh demonstrates the width of the hysteresis loop.푥̇1 and 푥̇2 are velocity values at the transition point between the pre and post yield region corresponding to 푥̈ < 0 and 푥̈ > 0, respectively. Also 푥̇1 and 푥̇2 can be defined from the chart.
푓푦−퐶푝푟푉ℎ 푥̇1 = (2.6a) 퐶푝푟−퐶푝표
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LITERATURE REVIEW
푓푦+퐶푝푟푉ℎ 푥̇2 = (2.6b) 퐶푝푟−퐶푝표
In order to accurately characterize the behavior of MR dampers using the nonlinear hysteretic bi- viscous model given by Equation 2.11 and 2.12, a set of four constant parameters that relate to the characteristic shape parameters to current excitation should be identified, and the set of parameters is as follows:
[,,,]ccfvprpoyk
Visco-elastic plastic Models
Generally, an MR damper operates in teo- rheological domains, that is, the pre-yield and post- yield regions. MR fluid is often considered to behave like a visco-elastic body in pre-yield mode and exhibits viscous behaviour in the post-yield region where the effects of inertia come into play. Thus a three parameter standard viscoelastic model was used to model pre-yield behaviour and a visco-elastic plastic was used to model the overall behaviour of the MR damper [49].
In this model the mechanism in both the pre- and post- yield regions were studied separately. By taking the station effect that results from the piston seal into consideration, the force component due to the pre-yield mechanism is given by
퐹 = 퐹푣푒 + 퐹푠 (2.7) where Fve is the visco-elastic force and Fs is the stiction force.
When the damper force is above the damper yield force Fy, the MR damper performs in the post- yield region. Both the fluid viscous residence and the inertial component contribute to the post- yield force. Thus, the damper post-yield force Fpost can be expressed as
퐹푝 = 퐹푐sgn(푥̇) + 퐶푦푥̇ + 푅푥̈ (2.8) where Cy is viscous damping coefficient and R is equivalent inertial mass, which depends on amplitude of displacement and frequency of vibration.
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LITERATURE REVIEW
The governing equation for this model can be expressed as
FFFFvesc F (2.9) CxRxFxFFvcc sgn()
Bouc-wen Models
The Bouc-wen hysteresis model possesses an appealing mathematic simplicity and is able to represent a large class of hysteretic behaviour [50]. The Bouc-wen model has been extensively used to simulate hysteresis loops because it can accurately portray force-displacement and force- velocity behaviour. The force in a nonlinear hysteretic system is divided into two parts:
Fxxgxxzx(,)(,)() (2.10) where g(x, x) is a non-hysteresis component that possesses a functional relationship with instantaneous displacement and velocity, α is a scaling value for the Bouc-wen model and z(x) represents the hysteretic component with respect to the time history of displacement. The evolutionary variable z is governed by
푧̇ = −훾|푥̇|푧|푧|푛−1 − 훽푥̇|푧|푛 + 퐴푥̇ (2.11) where z denotes the time derivative and the parameters , , A and n are used to define the hysteresis loop, respectvely. The scale and general shape of the hysteresis loop are governed by , , and A, while the smoothness of the force displacement curve is controlled by n. a) Simple Bouc-wen model A schematic of the simple Bouc-wen model is shown in Figure 2.5, and the damping force in this system is presented as follows:
F(t ) c 0 x k 0() x x 0 z (2.12)
where c0 and k0 are the viscous and stiffness coefficients, respectively, and the initial displacement x0 of the spring was incorporated into the model to present an accumulator, and z is an evolutionary variable defined in Equation 2.17. By adjusting the parameters of β, γ, A and n, the shape of the force-velocity characteristic can be controlled.
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LITERATURE REVIEW
The simple Bouc–wen model is well suited to numerical simulation because the resulting dynamic equations are not as stiff as those for the extended Bingham model. But it cannot reproduce the experimentally observed roll off effect in the yield region, i.e. for velocities with a small absolute value and an operational sign opposite the sign of the acceleration.
In order to accurately characterize the behavior of MR dampers by the Bouc-wen model, eight shape parameters must be decided, as follows:
ckxAn,,,,,, (2.13) 0,00
Figure 2.5 Schematic of simple Bouc-wen model b) Modified Bouc-wen Model In order to better assess the property of MR dampers in vibration control applications and make full use of the apparatus, a mechanical model was developed by Spencer et.al in 1997 to accurately describe the behaviour of the MR dampers [41], as Figure 2.6 shows.
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LITERATURE REVIEW
Figure 2.6 Schematic of modified Bouc-wen model
The governing equation for this model at constant electrical excitation are listed as follows
Force generated at upper section of the model
c1 y z k 0()() x y c 0 x y (2.14) where the evolutionary variable z is given by
zxy z||||() zxyzA ||() xy nn1 (2.15)
Solving Equation 2.20 derivative y can be derived as:
1 yzc xkxy 00() (2.16) cc01
The overall force is then given as
Fzcxykxykxx 0010()()() (2.17)
From the Equation (2.20), Equation (2.23) can be rewritten as
Fc ykxx110 () (2.18)
Comparing the modified phenomenological Bouc-wen model with the simple Bouc-wen model, an internal displacement y is introduced to the model to better capture the behavior of the damper in cases when velocities with a small absolute value and there is an operational sign opposite to the sign of the acceleration
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LITERATURE REVIEW
The five equations above present the mechanical status when the damper is taking constant magnetic excitation. But to decide for a model that is also valid at changing magnetic fields, the parameters dependent on the applied voltage or current must be determined. Therefore, the following relationships are given:
uu ab
ccuccu1111 ab (2.19)
ccuccu0000() ab where the first order filter u decides the dynamics involved in MR fluid reaching rheological equilibrium. And the functional relationship of u between the voltages applied to the damper is given as:
u u v () (2.20)
In summary, 14 parameters must be decided on in the modified Bouc-wen Model to accurately describe the hysteretic behavior of MR dampers.
(2) The Non-parametric Model The non-parametric modelling methods use analytical expressions to describe the behavior of an MR damper based on the testing data and the device’s working principles. The merits of the non- parametric modelling method are that they can avoid the pitfalls of parametric approaches while being robust and applicable to linear, non-linear, and hysteretic systems.
One of the most commonly applied non-parametric models is called the polynomial model. Ehrgott and Masri [51] assumed that the damper force could be written in terms of Chebyshev polynomials with respect to the damper velocity and acceleration. In this model, up to 64 coefficients must be identified, which time is consuming. Choi et al [52] proposed a six order polynomial to model an MR device with a satisfied match of model prediction and actual experimental data.
Other non-parametric models include the multi-function model [53], the black box model [54], and the query based model [55].
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LITERATURE REVIEW
2.3 ENERGY HARVESTING THECHONOLOGY The purpose of energy harvesting is to employ the mechanical energy resulting from vibration and shock motion into a power supply. The most widely involved in this subject is the mechanical – electrical energy converting system by magnet-electric induction [56]. These systems usually achieve this purpose by incorporating magnet or electromagnet induction, for some method, it is involved a necessary mechanical devices during the process. For applying on vehicle vibration reducing system, the energy that regenerated could be used in the suspension itself, or charge the battery directly.
Energy harvest achieved with rotary mechanism
The first category is to convert the linear damper vibration into oscillatory rotation and use rotational permanent magnetic DC or AC generators to harvest energy. A typical structure of this EHMR damper showed in Figure 2.7, including rack and pinion, ball screw, and hydraulic transmission, and so on. Such as, Avadhany et al [57] patented one type of rotary regenerative shock absorber based on hydraulic transmission. Choi et al [58] proposed an electrorheological (ER) shock absorber integrated with an energy generator by employing a rack and pinion gear mechanism, which converts a linear motion of the piston to a rotary motion, then activates a generator to produce electrical energy to self-power the excitation coil in the piston head. Li and Zuo [59, 60] proposed an energy-harvesting shock absorber with a mechanical motion rectifier (MMR), in the MMR, the roller clutches were embedded in two bevel gears and the function of ‘motion rectifier’ was achieved with a bevel gears mechanism. Yu et al [61] proposed a new type of energy-harvesting device system for the wireless sensing of inner-state conditions in the operation of MR dampers, where an impeller mechanism was used as the amplitude convert device, and an AC generator was applied as the energy converting part to convert the linear shock into electrical energy. Zhang et al [62] developed and prototyped a regenerative shock absorber based on a ball-screw mechanism and validated it with full-vehicle experiments in the lab. Guan et al [63] proposed a novel MR damper with a self-powered capability, the vibration energy harvesting mechanisms were adopted based on ball-screw mechanisms and a rotary permanent magnet rotary generator, to convert the external vibration energy into electrical energy to power the MR damping unit.
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LITERATURE REVIEW
Figure 2.7: A typical shock absorber with mechanical energy harvesting system [58]
It is noted that the energy harvesting achieved via rotary mechanism and commercial motor show a well performance and efficiency. The previous literature is generally based on the generating efficacy and feasibility of the energy recovery mechanism and MR damper. The size, weight of the device is usually unclear. In addition, due to the gap between assembly part in the mechanism, those devices is not sensate with the instant and micro change of amplitude and frequency. As the result, those drawbacks limit the application of the EHMR damper in some area such as self- sensing. Particularly, the large passive force that generated from motor and movement-transform components could bring a negative impact in semi-active dynamic control.
Energy harvest achieved with EMI mechanism
The second category is based on the design of an electromagnetic induction (EMI) device, which generates power from the relative linear motion between magnets and coils. As it is shown in Figure 2.8, this EHMR damper consists of a traditional MR damper and EMI system. Cho et al [64] proposed a special structure of an EMI device to be used with an MR damper. Choi et al [65] devised and investigated experimentala a smart passive control system comprising an MR damper
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LITERATURE REVIEW
and an EMI device to generate electrical power. Choi and Werely [66] studied the feasibility and effectiveness of a self-powered MR damper using a spring-mass EMI device. Sapiński established a special designed permanent-magnet power generator for MR damper, the designed vibration generator consisted a special arrangement and foil wound coil, the numerical analysis and experiment were carried out to address the magnetic field distribution and efficiency of the generator [67, 68]. Then, Sapiński proposed a multi-pole magnetic generator, the design of permanent magnets array was optimized, and both numerical method and finite element simulation was carried out to investigate the performance of the whole energy harvesting MR damper [69]. However, the large cogging force generated in the interaction between ferromagnetic components and permanent magnets array was recorded. This recorded cogging force could bring a negative impact to the dynamic control on the MR damper. Chen and Liao investigated a linear generator for a self-powered and self-sensing MR damper. The design of the power generator significantly minimized the cogging force and improves the dynamic damping performance [70]. The guild layer and shield layer were designed to isolate magnetic interaction effect between permanent generator and MR damper. However, the extra shield and guild layer increase the complexity of the whole structure while the component itself provides litter contribution to the dynamic control or generating effect improvement.
EMI system MR damper
Figure 2.8: A Typical EHMR damper based on EMI technology [64]
2.4 SELF-SENSING THECHNOLOGY Sensing structure using inducing coil
In the last several decades, the MR damper with sensing capability had been found in many studies. In order to maximum utilize the dynamic damping characteristics of the MR damper, as shown in
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LITERATURE REVIEW
Figure 2.9 (a), the dynamic response of the damper need to feed back to the system controller [71]. In the last decade, dynamic sensor, such as laser vibrometer and accelerometers, had been widely employed in real-time control of the MR damper. Pare 0 in the study of vibrattion controlling for vehicle suspension, proposed to obtain the dynamic response between the chassis and wheel by two accelerometers. The experiment result proved the high accuracy and large dynamic range of the proposed design, but the high cost of the system, especially the cost of sensor limited the application. Nehl [73] proposed to integrate the relative velocity sensor with controllable damper, which expected to use a static magnetic field of its integrated sensor. The experimental result proved the feasibility of this design. However, the proposed relative velocity sensor is difficult to integrate into a MR damper, due to the magnetic field interference between the static magnetic field and the one generated by MR damper. Chen and Liao [70] proposed a self-powered, self- sensing MR damper (SSMRD), which respectively integrated a linear generator and displacement sensor with MR damper. This design achieved to generate considerable power from vibration, also feedback the control system dynamically. Despite the separate design solving the magnetic field isolation between damper and sensors, the separate arrangement of generator and sensors increase the whole size of the device, which limited the use of the MR damper. Then Wang and Wang [74] proposed a principle and structure of integrated relative displacement self-sensing magnetorheological damper (IRDSMRD), which integrated the dynamic response sensor with MR damper. Although the proposed IRDSMRD accurately and dynamically respond, the proposed piston head could not fully utilize the magnetic field in the piston head, which limited the effect of the MR damper.
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LITERATURE REVIEW
(a) (b)
Figure 2.9 Self-sensing technology for MR damper: (a) MR damper with sensors control, (b) MR damper with EMI system [64, 65]
EMI structure integrated self-sensing capability
In many previous research, in order to make the best use of the dynamic damping characteristics of the MR damper, the dynamic response of the damper needs to feed back to the system controller. Those dynamic sensors, such as laser vibrometers and accelerometers have been widely employed for real-time control of the semi-active suspension system. However, relative velocity sensor is difficult to integrate into an MR damper, also the relative high-cost sensor could limit the application of semi-active MR damper.
In many current research, the possibility of achieving sensing by employing EMI device had been proven in many research. According to the Fraday’s law of induction, the alternating current can indicate the direction of movement of the MR damper and because the change in emf caused by the change in time rate is proportional to the relative velocity, the emf can be easily identified by the relative velocity across the piston of the MR damper. These theories have been widely used in inductive velocity transducers. This study aims to utilize the proposed EMI structure to provide the phase information of the velocity, rather than using a velocity sensor. The proposed design can also be used as an energy harvesting device. For this reason the self-sensing component is designed as a multi-functions structure. As a result, without utilized an extra sensing component, the energy harvesting MR damper could provide both self-sensing and energy harvesting capability. The result of this is a reduction in both the energy consumption and the size of the MR damper. The voltage generated by an EMI device could be used to present the relative velocity. Jung et al [75] employed an EMI device as a velocity sensor-sign sensor, investigating the sensing capability of the proposed EMI device incorporated in an MR damper-based vibration control system. Then Jung et al [76] developed a smart passive control system based on an MR damper and EMI device for a benchmark highway bridge model subjected to historic earthquakes. Followed, Jung et al [77, 78] developed the sensing capability of a MR damper-based system with an EMI device for common control method. Then Wang et al [79] developed a relative displacement sensing MR damper to integrate the relative displacement sensing and controllable damping. The prototype of
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LITERATURE REVIEW
such MR damper was fabricated and tested by Wang and Bai [80]. The principle of the developed device was based on frequency division multiplexing of the exciting coil and function multiplexing of the pick-up coil and the induction coil. Hu et al [81] investigated the static and dynamic performance of a self-induced MR damper. The theory of displacement differential self-induced performance was deduced. However, previous research saw the following drawbacks: larger size and weight cause by separate configuration, Complex device structure and modelling without considering their integration.
2.5 CHAPTER SUMMARY In this chapter, The key conceptions of MR technology and relevant conceptions were reviewed. Then the three main operating models of modern MR damper were presented. Followed, due to the non-linear mechanical property of MR fluid applied under external magnetic field, in order to determine the mechanical property, the basic conception of main mathematic models including the Bingham model, Bouc-wen model and their relative modified mathematic models was briefed and discussed. Secondly, the two main categories of energy harvest method include the rotary mechanism and EMI mechanism were presented. In this part, the conception, research history and the remained problem of the two technologies had been briefed and discussed. In the last part, the review of self-sensing technology was carried out. In addition, the drawbacks of previous self- sensing structure and method were discussed.
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DESIGN OF AN EHMR DAMPER
CHAPTER 3 DESIGN OF AN EHMR DAMPER
3.1 KEY CONCEPTION AND WORKING PRINCIPLE In this chapter, the design considerations and design principle of energy-harvesting MR (EHMR) damper are presented. The design process of MR damper and linear generator was illustrated separately, as different method applied. Followed, the configuration of EHMR damper was presented.
To brief the principle of EHMR damper, the operation principle of the prototype will be presented firstly. Then the beneficial of the prototype will be illustrated. Following that, the principle of electromagnetic induction (EMI) was briefed, and then the operating principle of the linear energy regenerator was introduced.
3.1.1 The Operation Principle of the Prototype The EHMR damper is connected to a base and load unit which is supplied by a hydraulic system. Thus the test system can generate a controllable vibration. When the external vibration applied on the EHMR damper, the EHMR damper converted the energy into electricity. Then the converted energy will be storage by energy harvesting circuits and apply on driving current. The control current drove the coil of MR damper, generating magnetic field surrounded the piston of MR damper, then change the velocity of MR fluid and generator damper force, achieving the vibration control.
Figure 3.1 illustrates the cross-section schematic of the proposed the EHMR damper. The EHMR damper consisted of MR damper and linear power generator parts. For the damper parts, there are two chambers in the cylinder, and the chamber is separated by a floating piston. The chamber with the piston is filled with MR fluid; and the other chamber is used as an accumulator to compensate the volume changing during the piston moves. The accumulator consists of a compression spring utilized to support the movement of a floating piston. As the piston rod moves, the MR fluid in the cylinder flows through the annular gap between piton and cylinder, the damper works in direct shear model. The excitation coil installed on the piston is electrically insulated. When a DC current was applied on the excitation coil, a magnetic field is generated around the coil and the piston head.
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DESIGN OF AN EHMR DAMPER
Then the annular gap would become an activated area, changing the viscosity of MR fluid in the gap, achieving the changing of damping force.
Figure 3.1 The schematic of EHMR damper
The linear power generator was radically arranged inside of the MR damper. Each two permanent magnets are separated by a spacer; also a magnet and a spacer combine to be a pole pair. There are totally eight pairs of magnet-spacer combined screw on the shaft. The inducing coil was arranged on the winding base. The phase of the generated voltage depended on the magnetic field distribution. The phase angle is 90o between each nearby coil. Each two different phases of coil were connected together to increase the efficiency of power generating. In this design, the 0o and 180o phase coils connected together, combing the coil A; also the 90o and 270o connected together, combining the coil B. Thus, the 14 phase coils design in the wending base, combined into two inducing coils (Coil A and Coil B). When the interaction between permanent magnets and coils occurred, the vibration energy will be converted into electrics into coil A and coil B.
3.1.2 Consideration in Structure Design Single ended structure
In this research, the proposed design was composed of a MR damper and a linear power regenerator. For the MR damper part, there are two common structures: single-ended and double- ended structures. The difference between the two structures is shown in Figure 3.2. For the single
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DESIGN OF AN EHMR DAMPER
ended structure, accumulator and float valve are needed due to the changing of volume during the piston, and piston was moving. The accumulator was proposed to solve this issue. While, for the double ended structure, because the volume of the MR fluid stay the same, the accumulator is unnecessary in this structure, but this structure would need nearly double axial space compared with single ended structure. Therefore, even the accumulator needed in single-ended structure of the MR damper increase the complexity of the damper, it provided a flexible axial design, also, convenience in manufacturing and assembling.
Piston rod under double- Piston rod for single- ended
ended structure Piston Operating Direction Operating Piston
Piston under single- Accumulator Piston under double- ended structure ended structure
Single-Ended Double-Ended Structure Structure
Figure 3.2 The difference between single-ended and double-ended structure
Magnetic Field Interference Isolation
As it is mentioned above that to avoid the magnetic-field interference between MR damper and generator, Chen [70, 89] proposed the structure called the flux guided land flux shield layers. The result shown in Figure 3.3 (a) presents the simulation of the flux under no proposed structure, and Figure 3.3 (b) presents the efficiency. However, the extra structure cannot be utilized by the damper or the generator; also the guild layer and shield layer improve the complex on
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DESIGN OF AN EHMR DAMPER
manufacturing and assembling. Therefore, it is valuable to propose a new structure which fully utilized the part of a damper, also minimized the magnetic interference.
Figure 3.3 The simulation of linear generator from Chen
The simulation of proposed structure shown in Figure 3.4, the proposed structure utilized the coils and coils base and the piston rod as the structure to guild the magnetic flux. As it is shown in the figure, as the coils base and piston rod are designed for magnetic-field interaction, without extra component, the magnetic-interference is minimized.
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DESIGN OF AN EHMR DAMPER
Core Air gap Magnetic flux Pole Piston rod Piece
Magnet MR fluid
Figure 3.4 The simulation of isolation of magnetic interference
3.2 MATERIALS USED IN DESIGN The MR fluid that used in this study is a kind of hydrocarbon-based MR fluid, the properties database on MRF 132 DG. The yield stress of this material is obtained from the value of the magnetic field strength. The properties of this material are shown in Figures 3.5, 3.6 and 3.7. Observing the three figures, the MRF shows a large yield stress under magnetic field while having a relatively low yield without magnetic field. This property could bring a rapid response and broad dynamic yield strength.
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DESIGN OF AN EHMR DAMPER
Figure 3.5 Shear stress vs. shear rate under no magnetic field applied [http://www.lord.com]
Figure 3.6 Yield stress vs. magnetic field strength [http://www.lord.com]
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DESIGN OF AN EHMR DAMPER
Figure 3.7 Typical magnetic properties
[http://www.lord.com]
Figure 3.8 Magnetic properties of steel 1020
[http://magweb.us/free-bh-curves/]
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DESIGN OF AN EHMR DAMPER
The high permeable material that used in this research is steel 1020. It provided a relatively high magnetic permeability also a high mechanical strength. Therefore, it is believed a desire material in parts that require magnetic permeability and high mechanical strength. The magnetic property is shown in Figure 3.8. The non-magnetic materials have low magnetic permeability. Non-magnetic materials that used are Acrylonitrile butadiene styrene (ABS) and aluminum which used to shield the magnetic flux to obtain the desire magnetic circuit. The magnet used in this study is neodymium permanent magnet. It is made from rare earth element, and keeps a high magnetic flux density. The permanent is NdFeB permanent magnet grand N52, the properties of this material is shown in Figure 3.9. This type of magnet is used in the linear generator.
Figure 3.9 Magnetic properties of NdFeB permanent magnet (N52)
[http://www.arnoldmagnetics.com]
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DESIGN OF AN EHMR DAMPER
3.3 CONFIGURATION OF THE EHMR DAMPER A typical single-ended MR damper [82] was shown in Figure 3.10. The damper piston inside the hydraulic cylinder house is the part to generate a magnetic circuit. The accumulator inside the base of the cylinder was utilized to prevent cavitation on the low pressure side of the piston in moving. The electromagnetic coils are installed in the piston head which is the main part to generate the magnetic field. When the excitation applied on driving coil, the MR fluid flows through an annular orifice in the piston head. Then the MR fluid will be magnetized by the magnetic field depends on the driving current applied.
MR fluid flow
Magnetic flux
Magnetic field
Gap
MR fluid MR fluid
Figure 3.10 Principle of operation of MR damper
3.3.1 Modelling of the MR Damper One of the critical designs of the EHMR damper is the magnetic circuit. Figure 3.11 illustrates the key diagram of a basic magnetic circuit 0, where gap h is MR fluid flow path. Considering the procurement, in this study, low carbon steel 1020 which could provide a relative high magnetic permeability, was used to act as the core. In order to maximize the magnetic field energy in the fluid gap and minimizing the energy loss, the principle in determining the parameter of electromagnetic circuit proposed by Arof [84] was applied. The excel spreadsheet given by Yang [85] was applied to assist designing.
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DESIGN OF AN EHMR DAMPER
Lc
Gap h Cylinder House
Damper Piston
Magnetic Chock
Figure 3.11 Key diagram of the basic magnetic circuit of MR damper
The key parameters of the cylinder of proposed damper are shown in table 3.1
Table 3.1 Key parameter of the cylinder
Parameter Value Parameter Value Diameter of cylinder Diameter of coil 20 mm 29 mm (D1) space (D3) Length of piston rod Diameter of piston 121 mm 79 mm (L1) (D4) Inner diameter of Stroke valve(L) 36 mm 81 mm cylinder (D5) Outer diameter of Diameter of cylinder 36 mm 91 mm piston rod (D2) (D6)
Theoretical analyses of performance of piston rod.
The material of the valve is steel 1020, which the Fy is 235Mpa.
퐹 휎 = max (3.1) max 휋푅2
휎=3.18 Mpa < Fy.
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DESIGN OF AN EHMR DAMPER
The Table 3.2 illustrated the key parameter of the piston
Table 3.2 Key Parameter of the Piston
Parameter Value Diameter of inner tank 81 mm Diameter of coil space 79 mm Diameter of piston 50 mm Inner diameter of tank 81 mm Outer diameter of tank 91 mm Gaps of Magnetorheological fluid 1 mm
Length of gallery 9 mm
Weight of coil space 18 mm
According to the τy-H curve, it is demonstrated that the τmax of MRF 132 DG is 60 kPa, where the H is 232 A/m, also according to the B-H curve, when the stress of magnetic field is 0.6T, the maximum of yield stress occurred. Therefore B=0.6 T is the magnetic saturation point. The structure of piston head is shown in Figure 3.12.
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DESIGN OF AN EHMR DAMPER
L Damper MR flow housing
A7
A5 A6
A3 A4I
5
4
R R
3 Magnetic
R A2
2 flux circuit
R 1
R Damper core A1
l b l
Figure 3.12 Structure of piston head
When B5=0.6T. The MR fluid in active area reaches the magnetic saturation. According to the following equation:
∅ = 퐵i푆i (3.2)
-2 In this situation, the magnetic flux in the area is ∅5=6.5×10e Wb. Then the ∅ in other areas is given in Table 3.3:
Table 3.3 Magnetic flux in each region of the piston
2 2 2 2 2 2 2 SA1/m SA2/m SA3/m SA4/m SA5/m SA6/m SA7/m 1.5×10e-2 4.4×10e-4 9.2×10e-4 9.2×10e-4 1.1×10e-3 1.1×10e-3 1.2×10e-4 Table 3.4 Magnetic induction intensity of each region
BA1/T BA2/T BA3/T BA4/T BA5/T BA6/T BA7/T 0.8 1.477 0.71 0.71 0.6 0.6 0.54 Then the magnetic field strength of each region was made and presented in Table 3.5.
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DESIGN OF AN EHMR DAMPER
The magnetic saturation of steel 1020 is 1.6 T, therefore, none of those parts reach the magnetic saturation before MRF.
Table 3.5 The magnetic field strength of each region
-1 -1 -1 -1 -1 -1 -1 HA1/AM HA2/ AM HA3/ AM HA4/ AM HA5/ AM HA6/ AM HA7/ AM
400 1250 232 232 300 300 300
𝑖 푁퐼 = ∮ 퐻푑푙 = ∑𝑖=1 퐻𝑖 푙𝑖 (3.3) where N is the number of turns, I is the current, H is the strength of magnetic field, l is the length of magnetic circuit component.
The current density J should be within:
J=5~12 A/mm2
Consider that the designed electro circuit could apply sinusoidal wave, the maximum current density should not be more than J=5~12 A/mm2 , also it is assumed that the maximum current is 1.5 A. Thus, the diameter of the wire is calculated by the given equation:
퐼 1.5 푑 = 2√ = 2√ = 0.437 푚푚 휋퐽 휋×10
Thus, according to the calculating result, the diameter of wire is chose in 0.5 mm. Then, the cross- section of the wire is calculated by:
푑 2 퐴 = 휋 ( 1) = 0.196 푙 2
Then the maximum number of turn is obtained. Considering the space between wire in the coil, the number of turn is constant as 250.
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DESIGN OF AN EHMR DAMPER
3.3.2 The Simulation Based on Finite Element Method To accurately visualize magnetic field strength, the ANSYS was involved in the magnetic field analysis based on finite element method. It is conveniently to make a half-size damper piston model and analysis by using the APDL common flow integrated in ANSYS software.
Figure 3.13 illustrates the finite element model and static electromagnetic field simulation of the MR damper part. Figure (a) presents the finite element model of the damper part. The leakage of magnetic flux had been considered in the simulation to acquire reliable magnetic field distribution for the piston head. The model includes the piston head, the piston rod, the excitation coil and the resistance gap, and the piston head is made of steel 1020 which provides a high magnetic permeability. Figure (b) shows the magnetic flux of the MR damper part. It can be seen that the magnetic flux vertically passing through the annular gap, which means the high efficiency of magnetic field. Figure (c) illustrates the magnetic flux density of main area for the MR damper part, the maximum magnetic flux intensity 1.62T is saw in the piston, while still less than the magnetic saturation of steel 1020. The magnetic flux density within the annular gap is ranged from 0.55 T to 0.74 T when the excitation current was set as 1 A, which leading to generate a large damping force.
Figure 3.14 shows the magnetic flux density of the annular resistance gap under the different applied current. As showed in the figure, the magnetic flux density increased as the applied current increased. The most efficient energy utilization point occurred at 0.6 A, and the magnetic saturation point is occurred at the point of 1 A excitation.
Figure 3.15 shows the magnetic flux density under different current excitation. As it is seen in the figure, the magnetic flux density reached the most efficient value in the two activated sections when the driving current applied. Due to the value of density reached stable in the activated areas. It can be concluded that the proposed design could utilized the magnetic field efficiently.
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DESIGN OF AN EHMR DAMPER
Piston rod
Cylinder
Excitation coil
Piston head
MR fluid
(a) (b) (c)
Figure 3.13: Finite element analysis of MR damper part: (a) finite element model, (b) magnetic flux distribution, and (c) magnetic flux density
0.6
(T) B 0.4
0.2
Manetic flux density density flux Manetic
0 0 0.3 0.6 0.9 1.2 Current I(A)
Figure 3.14: Magnetic flux density under different applied current
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DESIGN OF AN EHMR DAMPER
0.6 0.2A 0.4A 0.6A 0.4 0.8A 1.0A
0.2
Magnetic flux density B (T) 0.0
0 5 10 15 20 25 30 35 Length L(mm)
Figure 3.15 Magnetic flux density in the annular gap under different currents
3.4 CONFIGURATION OF LINEAR POWER GENERATOR As Arof [84] discussed the finite element method used in design and optimize the performance of tubular permanent magnet generator, and the benefit of slotless linear generator had been discussed by Chen [89], the generator that utilized in this study is a slotless generator based on the following reason:
The material of the base would determine the maximum and minimum magnetic flux density in the coils when interaction between magnets and coils occurred [90]. Thus, the cogging force is generally generated by the interaction between the magnets array and the slotted material, especially the teeth of the coils base. In this study, the overall damping force consists of the damping force from damper part also the cogging force from the generator part. However, the force from damper part was controlled by the excitation driving voltage, while the cogging force from the generator was uncontrollable. Thus, the cogging force should be minimized to benefit the control of the whole damper.
In this study, some conclusion from previous research of Sapiński [69] and Chen [70] were cited, the nonmagnetic material was utilized in the proposed generator. The simulation from ANSYS
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DESIGN OF AN EHMR DAMPER
and the experiment shown that, the cogging force provided minimized impact on the damper’s control. In order to illustrate the efficiency of this structure, the measurement of cogging force will be involved in this study.
3.4.1 Modeling of Linear Generator The main component and schematic is shown in Figure 3.16. As the principle had been discussed before, the adjacent coil could convert the vibration energy into electricity when the interaction between magnet and coils occurred. Compared with the power generator proposed by Sapiński [67] which utilized the spacer to guild the magnetic flux with a high magnetic permeability, the magnetic flux will go through coils and coil bases with the low permeability in this structure.
S Inducing coil A Vibration N
Inducing Sharft coil B N Piston rod Magnet S Winding base Pole pitch Magnetic S flux τm Wt τ N
g δw S lm D
Figure 3.16 Schematic of linear power generator
The equivalent magnetic circuit of the proposed generator structure is shown in Figure 3.17. Table 3.6 illustrates the material of each main component. The parameter of the main structure is shown
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DESIGN OF AN EHMR DAMPER
in Table 3.7. The total number of magnets is determined to be 8, and 14 coils were installed for the electromagnetic working range.
Table 3.6 material used in main component
Part Material Outer base for permanent magnet 1020 Permanent magnet NbFeB 53 coil brass
Table 3.7 parameter for main structure
Thickness 10 mm Magnet Height 5 mm Number 8 Thickness 2 mm Pole piece Number 8 Gap Gap distance 0.2 mm Maximum current 1.5 A Coil Wire turns 32 thickness 0.5 mm
Theoretical analyses of reluctance:
푙𝑖 푅𝑖 = (3.4) 휇𝑖푆𝑖
Where li is the length of magnetic circuit component, Si is the cross section area of components, μi is relative magnetic permeability.
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DESIGN OF AN EHMR DAMPER
Rcore
Rpole Rpole
Rpole Rpole mmf
Rmag/2 Rmag/2
Rleak
Figure 3.17 Equivalent magnetic circuit for the proposed power generator
Then according to the B-H curve, the peak voltage E can be calculated by the following equation:
퐸 = 퐵푙푣 (3.5) where B is the magnet induction, l is the length of coil, v is velocity when coil moving in magnet field.
The current without considering the current resistance can be calculated by:
퐼 = 휎퐵푟푣푟퐴푤 (3.6) where σ is the conductivity (S/m), Br is the magnet induction in radial direction (T); vz is the relative 2 velocity when coil move in axial direction (m/s), Aw is the cross-section area of coil (mm ).
푙 = 휋퐷푐푁 (3.7) where Dc is the average diameter of coil, N is the number of turns.
Then the peak voltage for each turn of coil can be calculated by:
2휋퐵 푣 퐷 퐴 퐸 = 푟 푧 푐 푐 (3.8) √3푑2
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DESIGN OF AN EHMR DAMPER
3.4.2 The Simulation Based on Finite Element Method Figure 3.18 illustrates the finite element analysis of the linear power regenerator. Observing Figure 3.18 (a), the main components of the generator include shaft, the permanent magnet arrays, the air gap, winding base and inducing coils, the environment includes piston rod and MR fluid. There are two arrangements for the permanent magnets: 0o phase, and 180o phase. Each two opposite arranged magnets are represented by a spacer. In order to investigate the magnetic interaction between the linear power generator and the damper, the magnetic flux leakage had been considered. Figure 3.18 (b) shows the magnetic flux distribution. As it is seen, the magnetic flux through the gap between magnet array and piston rod. As the result, inducing coils installed in winding base can generate induced voltage when the interaction between magnet arrays and inducing coil occurred. Figure 3.18 (c) shows the magnetic flux density distribution. In this simulation, it is seen that the magnetic field well fit the theoretical design shown in Figure 3.21. The simulations prove the feasibility of the proposed design.
(a) (b) (c)
Figure 3.18 Magnetic Flux Density Distribution
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DESIGN OF AN EHMR DAMPER
The distribution of cogging force of the proposed structure is calculated by ANSYS. The process of magnetic force computing is based on Maxwell stress tensor and virtual work methods. The overall computed cogging forces is 8 N, and the distribution is shown in Figure 3.19. The generator would have little impact on the damping performance, since the cogging force is small.
Magnet force distribution
Figure 3.19 cogging fore distribution
3.5 DEVELOPMENT OF A SELF-SENSING ALGORITHM The sensing capability is a way to provide the information of velocity and displacement. The sensing component of the damper can directly obtain the generated voltage. By utilizing sensing function, relative velocity between piston and cylinder was aquired. Then, the relative displacement could be also acquired. The information could be used in different control algorithms,
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DESIGN OF AN EHMR DAMPER
such as skyhook algorithms [91]. Then it can improve the performance of the MR damper in various vibration-control areas.
The numerical analysis was carried out to address the magnetic property for only one pole pair. It can be assumed that the reluctances of the pole spacer are neglected for their high magnetic permeability, thus the magnetic flux is given as [92]:
BmHA = remm0cc g A 2+gBmH g remm0c A m (3.9) where Φg is the magnetic flux of air gap without considering the leakage, μ0 is the relative magnetic 2 permeability, and equals 4π×10e-7 (N/A ), Hc is the magnetic field intensity of magnet, Brem is the flux density of the magnet, Ag is the surface area of cylindrical air gap, Am is the cross-section area of magnet, and Ag and Am could be obtained by:
g+ w Aslgmm (3.10) 2
Asls 2 2 mm (3.11)
The induced voltage E in the inducing coil is defined as
dz ENz g sin dt (3.12)
2A N c 2 3d (3.13) where N is number of turns of the inducing coil, E is the peak voltage in the inducing coil, Ac is the cross-section area of electrical wire, d is the diameter of the wire, τ is length of the pole spacer, z is the displacement, dz/dt is the velocity, and θ is the initial phase angle of inducing coil.
And because the phase angle between coil 1 and coil 2 is 90o, the voltage in coil 2 could be rewritten as the following equation:
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DESIGN OF AN EHMR DAMPER
dz ENz g cos dt (3.14)
Considering that the initial position of the magnets may not match the zero position of the coil, the initial relative displacement need to be added in the equation. Then, in order to fit the phrase position of coil 1 and coil 2, the Equation 3.14 can be rewritten as:
dz ENzz1 gisin() (3.15) dt
dz ENzz2 gicos() (3.16) dt where zi is the initial position of magnet array related to the zero position of coils.
The information obtained from coils is voltage value and frequency, thus compared with the self- sensing method from Wang and Chen which can acquire the information directly, the sensing algorithm must be utilized.
According the equation 3.20 and 3.21, it is easy to find that:
222222 dz EENzz12 () [sincos]()g (3.17) dt
Then, it is easy to have the relations between velocity and voltage:
dz EEN2222 ()() (3.18) 12 g dt
Furthermore, the equation be rewritten as:
dz EE22 || 12 (3.19) dt ()N 2 g
Base on the equation, the algorithm is developed. The velocity-sensing algorithm is shown in
Figure 3.20. The squared value of E1 and E2 are used to obtain the absolute value of velocity |dz/dt|.
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DESIGN OF AN EHMR DAMPER
Then the absolute value is assumed to two different sign of possible velocity. Sum the two obtained value of velocity respectively to acquire the guessed relative displacement z1 and z2. And then, substitute the guessed velocity and displacement to Equation 3.19 to compute the guessed velocity
E11 and E12. Compare the error between E11, E12 and initial measurement of voltage E1. The value with smaller error provides the preliminary direction information. After the continuous detection, the complete velocity information can be obtained.
t=0, z
t=t+dt
Eq. (3.27)
|dz/dt|
|dz/dt|=|dz/dt| |dz/dt|=-|dz/dt|
Z1 Z2
Eq. (3.23) Eq. (3.23)
E11 E12 |dz/dt|=-|dz/dt|
NO |E11-E1|<|E12-E1|
Yes
dz/dt=|dz/dt|
Yes NO Sign (dz/dt) keeps continuity
Figure 3.20 The principle of velocity-sensing algorithm
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DESIGN OF AN EHMR DAMPER
3.6 CHAPTER SUMMARY In this chapter, the general information of energy regenerative MR damper and considerations in the design were presented first. Then the operation principle of the proposed EHMR damper was introduced. A short paragraph following highly citing the preview design then introduces the improvement of the proposed structure.
In the design part, the materials that used in the proposed prototype had been briefed. The modeling of the MR damper based on the finite element method had been developed. The developed model was tested in ANSYS and the desired magnetic strength had been discussed. Then the model of damping force based on Bouc-wen model had been investigated. Followed the desired damping force was given by unsing Simulink from Matlab.
Then the design linear generator was discussed. The finite element model for the linear power generator was built in ANSYS. Then the finite element analysis based on Maxwell method was carried out to investigate the characteristics of design magnetic field. Followed, the effect of the magnetic interference had been discussed. Then the distribution of cogging force was discussed. At last the numerical method for self-sensing capability was developed and discussed.
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CHAPTER 4 PROTOTYPING AND TESTING OF EHMR DAMPER
In this chapter, first the structural design of the EHMR damper was described. Then simulation of magnetic field institution base on the finite method was discussed. Followed, the fabrication of prototype was presented. Next, the excitation current generator for the MR damper was introduced, and the discussion of the (Materials Testing System) MTS 647 system and NI USB-6259 DAQ board that used in the experiment was presented. The result of the testing had been done with the proposed EHMR damper. Firstly, the relationship between damping force and displacement was presented and discussed. Other key issue such as the changing of damping force outputting under different frequency and displacement without driving current was discussed, then the damper's performance that works under 0, 0.8, 1.6 and 2.4 V driving voltage was investigated. The evaluation of the damping force model was investigated. In the next section, the performances of the linear generator were presented, the relationship between time and generated voltage without and after rectification were discussed. The performance of the proposed generator working under several of excitation displacement and frequency were investigated. In the following section, the self-sensing capability based on the proposed structure was investigated.
4.1 FABRICATION AND ASSEMBLING OF PROTOTYPE The MR damper used in this study was tested in a hydraulic MTS system. The prototype is manufactured by the workshop in the University of Wollongong. The main components of the proposed EHMR damper shown in Figure 4.1, consist of a MR damper, and a linear energy regenerator which integrated into the piston rod. The rubber sealing O-rings was utilized as the main sealing parts in this prototype.
The key designs in the prototype are the sealing issue the compression spring used in the accumulator.
Because the interaction between the outer cylinder and piston, piston rod and floating valve, the MR fluid could leak, especially when the MR damper operating under high shear rate caused by driving current. In order to deal with the first issue, the critical parts of the prototype were utilized the interference fitting, such as the piston and the piston rod. Because the MR damper was tested
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PROTOTYPING AND TESTING OF EHMR DAMPER
in low frequency [91, 92, 94], for the sealing parts used in where the interaction could occur, different size of sealing was utilized.
Another key design is the accumulator. In the commonly accumulator design, the component of an accumulator is a cylinder that contend a certain amount of high pressure gas [20], the other design is chamber which consist of compressed spring. And the two strategies applied in preventing the volume changing during the piston moving around. Considering the feasibility of manufacturing in the workshop, in this study, the compression spring was involved in the proposed design.
Cylinder
Winding Floating Base Valve
Lower Piston Rod Cover
Upper Screw Cover
Shaft with magnets array
Figure 4.1 Main components of the proposed EHMR damper
The main component and assembly of the proposed MR damper part are shown in Figure 4.2. The parameter of the MR damper is shown in Table 4.1. The cylinder, piston head and piston rod are made of high magnetic material steel 1020. The piston and shaft of the generator are made of aluminum which is non-magnetic material, and the material used in spacers is steel 1020. The permanent magnet that used in the design is NdFeB magnet grade N 52. The magnets are stacked
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PROTOTYPING AND TESTING OF EHMR DAMPER
in pairs as Figure 4.2 (b) shown, the magnetic flux through the spacers under the driving of opposite magnetomotive forces.
(a) (b) (c) (d) Figure 4.2 The proposed MR damper: (a) piston head, (b) permanent magnets array and shaft;
(c) winding base of generator, and inducing coils, (d) the assembly
Table 4.1 Parameter of the fabricated MR damper part
Parameter Value Parameter Value Diameter of piston R 79 mm Pole pair thickness τ 9 mm Diameter of coil space Rc 50 mm Magnet Height lm 5 mm Thickness of cylinder Rh 5 mm Magnet Number 8 Gaps of Magnetorheological fluid h 1 mm Diameter of rod s 2.5 mm Length of piston L 28 mm Magnet Thickness τm 5 mm High of gallery Wc 9 mm Length of teeth wt 2 mm Length of gallery L1, L2 9 mm Thickness of piston rod δw 5 mm Number of turn N 250 Length of air gap g 4.5 mm Weight of coil space Lc 18 mm Coil Maximum current 1.5 A Electrical wire cross section ϕ0.5 m Coil Wire turns 256 Resistance of excitation coil 4Ω Coil thickness 0.5 mm Resistance per inducing Diameter of generator structure D 17 mm 4Ω coil
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PROTOTYPING AND TESTING OF EHMR DAMPER
4.2 TESTING PROCESS The fabricated MR damper was tested to obtain the property of the three proposed functions: controllable damping capability, sensing capability and generating capability. The input DC generator CPX400A provides a controllable DC voltage and current. Under excitation, the MR damper can generate a controllable magnetic field in the cylinder. The MTS 647 system can provide controllable frequency and displacement input, and flexible force. By appling a constant or flexible excitation, the MR damper can generate a controllable damping force. The damping force is measured by the MTS system. The generated electrical voltages from the two coils of the generator and sensing voltage are measured and recorded by NI USB-6259 DAQ. Then the voltage signal was processed by a PC to estimate the relative velocity.
The MTS setup with the EHMR damper is shown in Figure 4.3. One end of the prototype is fixed, while the other end is driven by the load unit. The MTS connect with a hydraulic system by tubes. And the EHMR damper is connected with MTS by gripping device.
Force Load Unit Transducer Crosshead Upper Grip Load Unit Columns MR Damper
Hydraulic Pressure Return Tube
Lower Grip
Figure 4.3 Main components arrangement for the prototype testing
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PROTOTYPING AND TESTING OF EHMR DAMPER
4.3 THE PERFORMANCE OF EHMR DAMPER In this section, the overall properties of the proposed MR damper was tested. In order to evaluate the damper's outputting characteristics, the MR damper part was separated from the EHMR damper. In the following discussion, first the relationship between damping force and displacement was presented and discussed. The properties of damping force outputting was test under different amplitudes and frequency. The range of excitation amplitude was constant in 1mm, 2.5mm, 5mm and 7.5mm, and the frequency was 1 Hz to discuss the relationship between output damping force and amplitude. Then the excitation frequency was constant in 0.1 Hz, 0.5Hz, 1Hz, 2Hz and 3Hz, working under amplitude of 5mm to discuss the relationship of the changing of force output and excitation frequency. To exam the output property of the proposed MR damper part, the output characteristics under different excitation voltage were tested and presented. In the last part of this section, the proposed Bouc-wen model was tested and discussed.
4.3.1 Testing of the Damping Property The MR damper was tested under different excitations. The first experiment was carried out to find the performance of the MR damper under different amplitudes and a constant frequency. As it is shown in Figure 4.4, the driving current was set at 0 A, and the frequency was 1 Hz, the amplitude was set as 1mm, 2.5mm and 7.5mm. In Figure 4.4, the driving current was 0 A. The frequency was set at 1 Hz. The force-displacement loop approximates rectangular shape. As it is shown in the figure, the maximum force output is from -250N to 250N, measured when the damper operated under 7.5mm amplitude, the minimum force output is from -200N to 200N, measured when the damper operated under 1mm amplitude. Because the frequency of the excitation was constant at 1 Hz, an increase the amplitude means to increase the input velocity. Thus it is clear that the damping force depends on the initial velocity driving the damper. Furthermore, because the cogging force that generated by linear generator is 8N in minimized. The cogging force has minimum influence on the damper’s performance and damper’s control.
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PROTOTYPING AND TESTING OF EHMR DAMPER
Figure 4.4 Damping force vs. amplitude under 1Hz frequency
Another experiment was carried out to analyze the characteristic of the damper’s performance under different excitation frequencies. In this experiment, the driving current was zero, the excitation amplitude was constant as 5mm, and the frequency was chosen as 0.1 Hz, 0.5 Hz, 1 Hz, 2 Hz and 3 Hz to obtain the performance characteristic of the proposed MR damper. As it is seen in Figure 4.5, the maximum output force is from -320N to 300N, measured when the damper operated on 3 Hz; the minimum output force is from -220N to 220N, measured when the damper operated under 0.1 Hz. Because of the amplitude was constant, the changing of the frequency means changing the velocity, thus, it could be summarised that, when the MR damper operated under passive model, the damping force depended on the excitation velocity.
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PROTOTYPING AND TESTING OF EHMR DAMPER
0.4
0.2
(kN) 0.1Hz
F 0.5Hz 0.0 1.0Hz 2.0Hz 3.0Hz
Damping force -0.2
-0.4 0 1 2 3 4 5 Displacement s(mm)
Figure 4.5 Damping force vs. excitation frequency under 5mm amplitude
1000 0A 0.2A 0.4A 0.6A
500
0
Damping force (N) -500
-1000 0 1 2 3 4 5 Displacement (mm)
Figure 4.6 Damping force vs. excitation current under 5mm amplitude
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PROTOTYPING AND TESTING OF EHMR DAMPER
1000 0 A 0.2 A 0.4 A 0.6 A
500
0
Force(N)
-500
-1000 -20 -10 0 10 20 Velocity (mm/s)
Figure 4.7: Force-displacement relation of the MR damper test with different current under 1 Hz, 5mm amplitude
The damper’s operating properties under different driving currents were obtained by changing the input current excitation. In this experiment, the frequency was set as 1 Hz, the excitation amplitude was set a constant value of 5mm, and the DC current excitation was set as 0 A, 0.2 A, 0.4 A, 0.6 A respectively. The result of the proposed experiment was illustrated in Figure 4.6, from this figure, the maximum output force is from -740N to 700N, measured when the damper operate under 0.6A; the minimum output force is from -220N to 220N, measured when the damper operate under 0 A. Because the amplitude and frequency were constant, changing the driving current will changing the strength of magnetic field on the piston and flow gap. Thus the viscosity of MR fluid flow through the flow was changed depended on the applied magnetic field. A larger damping force was obtained by increasing the DC current.
It is noted that the force decrease is observed in Figure 4.6, when the damper operated under 0.6A. There are two reasons for the observed issue. The first is the compressibility of the trapped air. Instead of using high pressure air which commonly found in Lord’s design, the compression spring was utilized as the main component to drive the float valve to avoid the volume change during the damper’s operating. However, as the stiffness of the compression spring was constant, lag and lack
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PROTOTYPING AND TESTING OF EHMR DAMPER
of stiffness were seen in this experiment. Secondly, due to the machining precision, a slight fluid leakage occurred during the test. Both factors cause vacuum jounce during the damper operated under high pressure.
Figure 4.7 illustrates the force velocity response under various excitation current of 0 A, 0.2 A, 0.4 A, and 0.6 A. The frequency was set as 1 Hz, and amplitude was set as 5mm. The maximum velocity of 17 mm/s was recorded, when the MR damper operated under 0.6 A excitation.
4.3.2 Modelling of Damping Force The force modelling based on Bouc-wen model [86-89] is developed for the proposed EHMR damper. The mathematical model is shown in Figure 4.8. The 14 parameter of the mathematic model is optimized by Simulink in Matlab. The program for the developed mathematic model is shown in Figure 4.9, and the optimized 14 parameters are given in Table 4.2. The corresponding mathematic expressions are given as follows:
FCykxxdd110 d () (4.1)
1 y[ z c xd k ( x y )] d ()cc d00 d d 01 (4.2)
nn1 zxyzzxyzAd ||||()ddxy ||() dddddddd (4.3)
I ab (4.4)
ccI11 c1 ab (4.5)
ccI00 c0 ab (4.6)
Where Fd is the generated force by proposed MR damper, xd is the damper’s operating displacement; yd is an internal pseudo-displacement; I is a first order filter depend on the input current; u is the voltage applied on the coils. In this model, k1 is the stiffness of the accumulator; c0 and c1 respectively represent the viscous damping coefficients observed at high and low velocities; k0 is the gain to control the stiffness at large velocities; x0 is the initial displacement of
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PROTOTYPING AND TESTING OF EHMR DAMPER
spring k1 associated with nominal damper force due to the accumulator; γd, βd, and Ad are hysteresis parameters and the yield elements; α is the evolutionary coefficient. The optimized values are determined by fitting the model to experimental data.
F
x
Wen
- Bouc
y k0 c0
k1 c1
Figure 4.8 Mathematical model of MR damper based on Bouc-wen model
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PROTOTYPING AND TESTING OF EHMR DAMPER
Figure 4.9 Matlab program for the proposed mathematic model
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PROTOTYPING AND TESTING OF EHMR DAMPER
Table 4.2 Parameter of the damping force model
Parameter Value Parameter Value -1 -1 c0a 3258 N s m c1a 26937 N s m -1 -1 c0b 7873 N s (mV) c1b 66175 N s (mV) -1 -1 k0 3836 N m αa 11140 N m -1 -1 k1 1136 N m αb 39636 N m -2 x0 0.005 s γd 217130 m -2 n 2 βd 2405500 m -1 η 190 s Ad 66
Based on the experimental data, the nonlinear optimization was involved in the optimization of the parameters of the mathematical model. The parameters are estimated to minimize the error between the model predicted and experimental data force. The variance function was estimated as the object function. The error concerned is represented by the given function 퐽:
2 푚푖푛 퐽 = 푚푖푛 ∑(푓푒푥푝푒푟푚𝑖푚푒푛푡 − 푓푚표푑푒푙) (4.7) where fexperiment is the data of experimental force, and fmodel is the predicted force based on the mathematical model. The comparisons of damping force given by the model predicted and experiment was illustrated in Figure 4.10. The damping force is obtained under harmonic excitation of 5mm amplitude and 1 Hz frequency. The force-displacement relation was shown in Figure 4.11. According to the figure, the mathematical model could well fit the experimental data, and predicted force is matching the damper's behaviors.
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PROTOTYPING AND TESTING OF EHMR DAMPER
Figure 4.10 Comparison of mathematic model and experimental data base on time-force relation
800
400
(N) F Bouc-Wen model Experiment 0
Damping force -400
-800 0 1 2 3 4 5 Displacement s(mm)
Figure 4.11 Comparison of damping force based on Bouc-wen model and measurement under 0.6A excitation current
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PROTOTYPING AND TESTING OF EHMR DAMPER
4.3.3 Identification of Damping Force Modeling The Bouc-wen model [86] was widely used in dynamic MR damper [83-85, 87, 92-98]. Based on the experimental data, the parameters of the proposed mathematical model of the MR damper were estimated by using the nonlinear optimization. The error between the model predicted and experimental data force was given by the J function mentioned in section 4.1.2. In this section, the estimated force model was tested to evaluate the damping force when damper operated under different excitation voltage.
Figure 4.12 illustrates the initial data when the damper operated at 2.4 V excitation voltages. The Bouc-wen model was built in the parameter estimation in Matlab, Figure 4.9 demonstrated the detail of the program. The result of the optimization was shown in Figure 4.11. As saw in this figure, the red line represents the desired damping force based on proposed Bouc-wen model; the blue line represented the initial data. According to the calculation result, the maximum damping force from the proposed mathematic model is from -761N to 700N, the initial data show the maximum measured damping force is from -741N to 711N. Thus the proposed mathematical model illustrates the relations of force-displacement.
In order to test the proposed mathematic model, the data shown in Figure 4.12 are the desired damping force when the MR damper operated under different excitation voltage. To evaluate the proposed model, the voltage was set according to the driving current that used in the previous experiment. As it is mentioned in section 4.1.1 the resistance of the coil is 4 Ω. The excitation voltage were set as 0V, 0.8V, 1.6V, 2.4V, which efficiently equal to driving current. As seen in the figure, the optimized force-displacement loop is nearly elliptical; the maximum desired damping force is from -741N to 711N, while the minimum damping force is -190N to 170N.
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800 0A 0.2A 0.4A 400 0.6A
(N)
F 0
Force Force -400
-800 0 0.2 0.4 0.6 0.8 1.0 Time t(s)
Figure 4.12 Desired damping force from mathematical model vs. initial measured data
Figure 4.13 The desired damping force when piston operates under different excitation
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PROTOTYPING AND TESTING OF EHMR DAMPER
In the further test, the desired damping force and measured data were illustrated in Figure 4.14 to evaluate the mathematical model. The orthogonal-line data represent the reconstructed result from the mathematical model, while the triangle-line data represent the measured one. As it is shown in the figure, the maximum output from the model and measurement is similar. While the largest error from this model occurred when the current was 0.4 A. In this part, the maximum force is from -450N to 450N while the measurement given -400N to 400N. The other error occurred when excitation were 0 A and 0.2A. According to the measured data that mentioned above, the output force when the damper operating under 0A and 0.2A excitation is similar, while, a slight gap was seen in the mathematical model.
Figure 4.14 The desired damping force from mathematic model vs. the measured data
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PROTOTYPING AND TESTING OF EHMR DAMPER
4.4 THE PERFORMANCE OF THE ENERGY HARVEST CAPABILITY In this section, in order to evaluate the performance of the proposed linear generator, first the comparison of experimental data with simulation result was carried out. The experimental results from both the two coils that installed in the generator were presented. Second, the performance of the proposed generator operating under different vibration environment was present, the constant environment including different amplitude and excitation frequency, the amplitude was set as 5 mm, 10 mm, and 15 mm, and the frequency was set as 2 Hz, 3 Hz, and 4Hz. Then, the frequency multiplication effect Cheng [99] in the proposed experiment was discussed. At last, the proposed AC-DC rectifier was introduced, and the problem of the handmade rectifier was discussed, performance of the propose generator was investigated.
4.4.1 Performance of the Linear Generator The voltage of the two adjacent coils were used to describe the properties of the energy regenerator. The generated voltage from coil 1 and coil 2 were showed in Figure 4.15 and 4.16 respectively. The data were obtained at a frequency of 4 Hz and amplitude of 15mm. As seen in the figure, a well-fitting between the theoretical analysis and experimental results were obtained. Some differences between calculation and experiment were due to the smooth process. The reason is that, a large amount of noises exist in the initial data, those noises not only impacted the accuracy of the voltage measurement, but also impact the self-sensing capability in the following process. Thus to minimize the noise, some processes, such as adding a low-pass filter, have to involve in the data analysis.
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Figure 4.15 Comparison between experiment and calculation result: coils 1
Figure 4.16 Comparison between experiment and calculation result: coils 2
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PROTOTYPING AND TESTING OF EHMR DAMPER
In order to evaluate the properties of the proposed generator, further experiments were carried out. The first group of experiments were the energy regenerative property when generator operated under different amplitudes. In this group, the amplitude was set as 5mm, 10mm and 15mm, while the excitation frequency was constant in 2 Hz. As the result shown in Figure 4.17, when the generator operated under 5mm amplitude the maximum generated voltage is from -0.2 to 0.2 V.
Then the frequency of excitation was increased to 3 Hz and 4 Hz respectively to evaluate the generator’s property. The data shown in Figure 4.18 and 4.19 are generating properties when the generator operating under amplitude of 5mm and frequency of 3Hz, while the other group was set under amplitude of 5mm and frequency of 4Hz. As it is shown in Figure 4.18, the peak voltage is generally from -0.3 V to 0.3 V, due to the relatively small size of the generator. Then the frequency was increased to 4 Hz, as it is shown in Figure 4.19, no significant increasing effect was recorded.
Figure 4.17 Generate voltage under open loop: 5mm 2Hz
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PROTOTYPING AND TESTING OF EHMR DAMPER
Figure 4.18 Generate voltage under open loop: 5mm 3Hz
Figure 4.19 Generate voltage under open loop: 5mm 4Hz
When the amplitude was increased to 10 mm and 15 mm, a significant increase of the generated energy was acquired. Figure 4.20 illustrated the characteristics of performance of generator
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PROTOTYPING AND TESTING OF EHMR DAMPER
operating under 10 mm and different frequency. Figure 4.20 (a) presented that the maximum voltage is 0.45 V. As shown in Figure 4.20 (b), a significant increase of voltage generating was recorded when the excitation frequency was set as 3Hz, the peak voltage increase to 0.7 V. However, according to Figure 4.20 (c), it is seen that when increasing the input frequency from 3 Hz to 4Hz, there is a slightly increase to be seen, which is similar to the previous experiment. While in the following experiment, the amplitude was set at 15mm. As it is shown in Figure 4.20, the figure illustrates the energy generating properties when the generator operated under 2 Hz, 3 Hz, and 4 Hz. The generator’s performance under setting environment was shown in Figure 4.20. According to the figure, the peak voltage range -0.7 V to 0.75 V, which is slightly increased compared with the performance under 10mm. When the generator operated under 3 Hz frequency, the peak voltage was measured at 0.9 V, which is 0.3V higher than the result from 10mm one. Then in Figure 4.20 (C), the frequency increased 1 HZ, the generator operated under 15mm 4 Hz excitation. As it is shown in the figure, the peak voltage measured at 1.22V. An interesting issue was recorded in these experiments, as the amplitude increase to 10mm and 15mm, the wave of the generative voltage is not the typical sinusoidal wave. This is because the frequency multiplication effect. This issue was detailed in the following section.
(a)
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(b)
(c)
Figure 4.20 Comparison of generative voltage under different amplitude and frequency: (a) 10 mm and 15 mm 2 Hz, (b) 10 mm and 15 mm 3 Hz, (c) 10mm and 15 mm 4 Hz
4.4.2 Frequency Multiplication Effect The effect that mention above is because the excitation amplitude larger than the pole pitches (9mm in the prototype). When the magnets array moved more than value of 휏, the magnetic flux distribution changed. As the structure of the proposed linear generator shown in Figure 3.16, the magnets array combines by multi pieces of magnets, the magnets in the array generate the different magnetic flux density and flux direction. This effect determines the voltage wave when the interaction occurred between coils and permanent magnets array.
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PROTOTYPING AND TESTING OF EHMR DAMPER
To illustrate the effect, the experiment result is shown in Figure 4.20 and Figure 4.21. Excitations were set as 10mm and 15mm respectively. The frequency was constant at 4 Hz. But 8 peaks were seen in the two figures. In the previous experiment shown in Figure 4.18, when the amplitude was set at 5mm, the amplitude is smaller than the value of 휏. There are only four peak were recorded in one period. Thus, this is the equivalent to the multiplication of generated voltage frequency.
Figure 4.21 Frequency multiplication effect when generator operated under frequency of 4 Hz and amplitude of 10mm
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PROTOTYPING AND TESTING OF EHMR DAMPER
Figure 4.22 Frequency multiplication effect when generator operated under frequency of 4 Hz and amplitude of 15mm
It is citing previous research from Cheng [99], the frequency multiplication effect could increase the effect of overall harvested power. Therefore, in the future design and investigation, more properties of the frequency multiplication effect could be investigated.
4.4.3 Performance of Energy Harvest Effect via Rectification Because the coils install in the piston of the MR damper are equivalent as an electrical inductance, compare with AC voltage generated from the proposed generator. The DC voltage was a better value to evaluate the performance effect of the proposed generator. Thus, in the further application of using the generated energy, a bridge rectifier needs to be involved. Then, the relative experiment was carried out to evaluate performance of the generator.
The principle of the bridge rectifier is shown in Figure 4.23, two coils applied in the linear generator, thus six diodes and one capacitance were needed in the proposed bridge rectifier. The photo of bridge rectifier part was shown in Figure 4.24.
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PROTOTYPING AND TESTING OF EHMR DAMPER
In the proposed experiment, the vibration excitation was constant at 15mm 4 Hz. The output of the proposed rectifier was connected to DAQ board that mentioned in chapter three. The EHMR damper was installed in the MTS which provide the amplitude and frequency excitation. The photo presented the installation of the prototype. Because of the coils from the generator is short, the rectifier was adhered with the out cylinder of the damper. Then in order to prevent the noise signal from DC power source, the DC power source was set as off. However, there is still large number of noise in the recorded data. The reason of this issue was detailed in the following paragraph. The experiment result when the EHMR damper operated under 15 mm 4 Hz excitation was shown in Figure 4.25. The experiment result shows that under the mention vibration environment, the rectified DC voltage is 1V.
One interesting can be discussed is the noise in the output signal. As it is shown in Figure 4.25, there are a large number of noises in the single. There are two main reasons cause this issue. First one, because the rectifier used in the experiment is a handmade board, coil used in this rectifier connected each electrical component without considering the noise shielding, thus it is easily to generate noise signal in the coil then direct record in the DAQ board. Second, because the AC-DC convective circle was not designed for the noise reduction capability, thus the noise generated in coil and from the environment was directly recorded in DAQ without any process. To solve the first problem, it should use commercial rectifier as the AC-DC converter component, which provides a full design including noise shield. Then to solve the second problem, some signal process should be involved in the design, such as a low pass filter could reduce the noise in the output signal.
Coils 1 AC input +
DCoutput
Coils 2 AC input
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PROTOTYPING AND TESTING OF EHMR DAMPER
Figure 4.23 Schematic of the AC-DC rectifier
Figure 4.24 Assembled EHMR damper with AC-DC rectifier
Figure 4.25 The experiment result of performance of generator with AC-DC rectifier
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PROTOTYPING AND TESTING OF EHMR DAMPER
4.5 THE PERFORMANCE OF SENSING CAPABILITY
4.5.1 Comparison Between Guessed Voltage and Initial Measurement The experiment was conducted under an excitation which the amplitude is 15mm and a frequency of 4 Hz. Figure 4.26 shows the comparison of voltage value between the initial measurement and guessed result from sensing algorithm. As the figure shown, there are some slightly differences between the numerical calculation and initial measurement. This is because, the initial relative position of magnets array may not match the zero point of the coil. As the result, the multiply effect on voltage may not fully exist in the measurement data. Also due to the noise signal in the experimental data, the theory predicted result of voltage from equation 3.12 may not completely follow the experiment result.
Figure 4.26 Comparison between experiment and calculation result: coils 1
4.5.2 Sensing of Velocity and Displacement The experiments were conducted to test the performance of velocity sensing under different excitation. Figure 4.26 and Figure 4.27 show the comparisons between the theoretical velocity wave and sensing velocity. As it is shown in the figure, the sensing velocity agrees with the sinusoidal velocity. There is some slight difference. The difference mainly occurs when the
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PROTOTYPING AND TESTING OF EHMR DAMPER
frequency is small. The reason is the sensing method utilized measured voltage of the two generation coils, and the initial noises bring a less impact in the larger sensing voltage. In Figure 4.27, the sensing velocity agrees better than the data in Figure 4.26, this is because the measurement noise in the initial signal. By increasing the excitation, the output voltage increased. Thus less impact was seen in the data from a large excitation. Then the sensing relative displacement is obtained by integrating the sensing velocity:
푧 = ∫ 푧̇푑푡 (4.8)
Figure 4.28 and Figure 4.29 show the comparisons between sensing displacement and the measured displacement. As it is shown in the figure, the sensing displacement agrees with the measured data.
It can be concluded that, by utilizing the proposed sensing algorithm, the generated voltage can represented the velocity condition of the MR damper. Further, the velocity and displacement condition of the MR damper can be acquired. Thus, the sensing capability had been integrated into the vibration control system. Although the self-sensing method requires real-time signal process, extra mechanism and sensor are not necessary for obtaining sensing data. As the result, energy consumption cause by extra sensor and energy waste due to mechanism had been minimized. In addition, the size of the whole device had been reduced.
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PROTOTYPING AND TESTING OF EHMR DAMPER
1.2 Self-sensing Theoretical 0.8
0.4
(m/s) v 0.0
-0.4
Velocity
-0.8
-1.2 0 0.2 0.4 0.6 0.8 1.0 Time t(s)
Figure 4.27 Experimental Result of Sensing Velocity Under Excitation of 3Hz 5mm
0.6 Self-sensing Theoretical 0.4
0.2
(m/s)
v 0.0
-0.2
Velocity
-0.4
-0.6 0 0.2 0.4 0.6 0.8 1.0 Time t(s)
Figure 4.28 Experimental Result of Sensing Velocity Under Excitation of 5Hz 15mm
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PROTOTYPING AND TESTING OF EHMR DAMPER
6 Self-sensing Theoretical
4
2
(mm)
s 0
-2
Displacement Displacement -4
-6 0 0.2 0.4 0.6 0.8 1.0 Time t(s)
Figure 4.29 Experimental Result of Sensing Displacement Under Excitation of 3Hz 5mm
20 Self-sensing Theoretical
10
(mm)
s 0
-10
Displacement Displacement
-20 0 0.2 0.4 0.6 Time t(s)
Figure 4.30 Experimental Result of Sensing Displacement Under Excitation of 4Hz 15mm
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PROTOTYPING AND TESTING OF EHMR DAMPER
4.5.3 Discussion of Self-sensing Result As it is shown in figures above, there are some gaps between the measured data and sensing displacement. There are two main reasons contribute to this issue. The first is the signal processing. As Figure 4.3-3 shown, there are large number of noise existed in the initial data. Those noises cause losing of frequency information then finally failed to acquire the velocity in following sensing method. Thus, it had to utilize some signal process to obtain a clean data. However, processed data loosed the peak value. As the result, some disagreement between the sensing displacement and measured data is seen, especially in the top and the button. The second thing is the thinness of the teeth is not considered in the design. As the result, the peak voltage from generated data did not fully agree with the theoretically wave.
4.6 CHAPTER SUMMARY In this chapter, the fabrication of prototype was presented. Some key issues in the fabrication including the accumulator and compression spring were briefed. Then the experimental setup and the experimental process were introduced. Followed, the main facilities used in the experiment were briefly introduced. Later, experiments were carried out to evaluate the property of EHMR damper, including the damping property, energy harvest capability and self-sensing capability.
In the experiments for damping property of EHMR damper, the impact of excitation frequency and amplitude was discussed based on experimental results. It can be noticed that, for the proposed EHMR damper, the excitation frequency and amplitude had a little influence on output damping force. While the experimental results shown changing the excitation current could significantly increase the damping force, it has been recorded that the damping force range from 200N (0 A) to 750N (0.6A). The damper acquired the changing damping rate of 375%. Thus, it can be noticed the feasibility and energy efficiency of the proposed MR damper. Then mathematics damping force model based on Bouc-wen model had been developed and optimized. Parameters of the mathematical model were obtained by nonlinear optimization based on experimental data. Comparisons of damping force between model guess and experiment show that the developed mathematic model well agrees with the curve of the damping force. As the result, the feasibility and efficiency for the EHMR damper had been proven.
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PROTOTYPING AND TESTING OF EHMR DAMPER
Then experiments were carried out to address the power generating property. The performance of the proposed generator operated under different vibration environment was present, the constant environment including different amplitude and excitation frequency, the amplitude was set as 5 mm, 10 mm, and 15 mm, and the frequency was set as 2 Hz, 3 Hz, and 4Hz. Then the property of energy recovery capability was addressed by using a proposed AD-DC rectifier. It had been recorded that after the rectifier, the output power is about 1 V. In addition, the frequency multiplied effect had been recorded and discussed.
Then, sensing algorithms had been experimentally tested. In order to evaluate the feasibility and efficiency, the excitation was set at different frequency and displacement. According to the experimental result, both the sensing velocity curve and displacement curve well agree with the excitation data. Moreover, due to the self-sensing algorithms is based on the linear generator; the extra sensing component is not necessary, and the structure of the whole device is simplified.
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CONCLUSION AND FUTURE WORK
CHAPTER 5 CONCLUSION AND FUTURE WORK
5.1 CONSLUSION In many current research on self-sensing MR damper, the separated component such as laser vibrometer and other sensors are necessary in obtain the dynamic information of a MR damper. In previous research on energy harvesting MR damper, the large cogging force and magnetic field interference bring a negative impact on the dynamic performance. Therefore, the EHMR damper with a minimized cogging force and magnetic field interference was investigated. The proposed EHMR damper integrated the energy harvesting and self- sensing capability, which contributes to energy saving and less maintenances for the vibration control system.
In the thesis, the design of the EHMR damper was discussed. The power generating method and self-sensing algorithm for the proposed EHMR damper was investigated. The key design issues, including the components' integration, structure design, operating principle, magnetic flux flow for the piston and generator, materials and experiments setup were discussed. The result of the finite-element method showed the efficiency of the structure with minimized the magnetic field interference between damper part and the magnets array of the linear generator.
The MR damper was designed to provide the controllable damping force. The parameters of the MR damper part was identified by using a numerical method. And the finite-element method was utilized to investigate the distribution of magnetic density in the piston area, further provide the desired magnetic flux density on the annual gap when excitation coil applied under different current excitations. The result of finite element analysis of the piston shows that the piston could provide an efficient damping force control and well energy efficiency. Then mathematics model bases on Bouc-wen model for the proposed EHMR damper was developed and optimized. The numerical analysis based on the mathematic model was carried out to identify the characteristics of the damping force, and then verify the working range of the MR damper. The experiment results show that the proposed mathematic model well agree the damper’s performance under different current. In the analysis and experiment of property, it has been recorded that the damping force range from 200N (0 A) to 750N (0.6A). The damper acquired the changing rate of 375%. The damping performance depends on different amplitude and frequency was discussed. It was noticed
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CONCLUSION AND FUTURE WORK that, the proposed damper provided a limited adoption under the passive model, while provide a large range of dynamic force output under a relatively low energy consumption.
In the energy harvesting part, an electromagnetic linear power regenerator was designed for power generation. The proposed slotless linear power regenerator provides a low cogging force, and the magnetic field interference is minimized by the design shared component. The proposed structure provides a benefit on a better dynamic damping performance under different excitation. Experiments are carried out to identify the characteristics of power recovery. The experiments result show that the proposed generator can recover about 1.3 V AC voltages on each coil under 4 Hz and 15mm excitation. Then the frequency multiplication effect is proved and discussed. Then the AC-DC rectified was applied to the energy recovery process. The experiment shows that, after the processing of a proposed rectifier, the generator provides about 1V DC voltage.
In the self-sensing part, the algorithms numerical sensing method was developed and tested. The investigated self-sensing capability aims to obtain the velocity and relative displacement of piston base on the generated voltage. Modelling, mathematic analyses, and experiments were performed for the purpose. Experimental result showed that the proposed method could accurately illustrate the velocity and displacement at various frequencies and amplitude. Compare with the previous self-sensing design, the algorithms proposed in this thesis achieve the sensing of velocity and displacement without extra sensing component. As the advantage in this design, it can significantly reduce the size of the whole device, also the energy compulsions due to the sensing mechanism and sensor is unnecessary. In addition, due to the minimized cogging force, the velocity and displacement sensing components bring a low affection on the dynamic control of the MR damper.
5.2 FUTURE WORKS In the following work, the energy harvest damper with smart passive structure could be investigated. The method of improving of energy harvesting efficiency of EMI base device could be investigated. Methods of optimization in structure and size for MR base device should be investigated and developed. Furthermore, the smart passive suspension employed rotary motor could be tested and developed. And improving of self-sensing capability can be investigated.
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REFERENCE
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APPENDIX
APPENDIX A: DETAILS AND CONSIDERATIONS OF UESING MTS The MTS system used in this study is driven by hydraulic power system model 505.07-G2. The system consists of a hydraulic power supply/service manifold and hydraulic actuator and grip controller.
The grip controller used in the experiments is 370 load frame, model 370.02. This controller provides the manual control for the grip wedding and vertical motion. In addition, the controller can illustrate the hydraulic pressure in the grip and actuator device.
According to the user manual for the MTS 647 system, the minimum grip supply pressure according to the following formula:
1 2.22푇2(푙푏×𝑖푛) 1 푃 (푠푝푖) = [1.44퐿2(푙푏) + ]2 (4.1) 푐 퐴(𝑖푛2) 퐷2(𝑖푛)
1 2.22푇2(푁∙푚) 1 푃 (푀푃푎) = [1.44퐿2(푘푁) + ]2 (4.2) 푐 10퐴(푐푚2) 퐷2(푚푚)
The actual clamping force (Fc) applied to the specimen when desired, followed by the given equation:
퐹퐶 = 1.5푃퐴
Then the maximum torque versus axial load was abstained and shown in the following two figures.
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APPENDIX
(a)
(b)
Maximum torque versus axial load of the MTS 647
To consider the safety issue, the maximum input frequency was set as 4 Hz, and maximum amplitude was set as 15 mm.
The DC power resource used in the experiment is CPX400A PSU power supply. The single/dual DC PSU power channel provides the maximum 420 watts output for each channel. The outranging outputs up to 60V voltage and 20 Amps output currents, which fully fit the requirement of the experiment.
The DAQ used in the experiment is NI USB-6259. This DAQ provide up to 80 analog input at 16 bits, up to 48 TTL/CMOC digital I/O lines and two 32 bit, 80 MHz counter/timer. In the proposed experiments, the maximum input frequency is up to 4Hz, the DAQ is fully fit the requirement of the experiment.
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